Engineer Justin Moresco (right) of RMS looks over a hole created by the earthquake in Napa, Calif. Risk Management Solutions (RMS) is a group of professionals that look at structural damage, liquefaction zones and interviews to determine the cost of the damage from an earthquake like the South Napa event. less

Engineer Justin Moresco (right) of RMS looks over a hole created by the earthquake in Napa, Calif. Risk Management Solutions (RMS) is a group of professionals that look at structural damage, liquefaction zones ... more

Chesley Williams (right) of RMS checks out some road and sidewalk damage on Meadowbrook Drive Tuesday August 26, 2014 in Napa, Calif. Risk Management Solutions (RMS) is a group of professionals that look at structural damage, liquefaction zones and interviews to determine the cost of the damage from an earthquake like the South Napa event. less

Chesley Williams (right) of RMS checks out some road and sidewalk damage on Meadowbrook Drive Tuesday August 26, 2014 in Napa, Calif. Risk Management Solutions (RMS) is a group of professionals that look at ... more

On Twin Oaks Drive in Napa, Calif. a utility worker makes repairs near a red tagged home the RMS group is investigating Tuesday August 26, 2014. Risk Management Solutions (RMS) is a group of professionals that look at structural damage, liquefaction zones and interviews to determine the cost of the damage from an earthquake like the South Napa event. less

On Twin Oaks Drive in Napa, Calif. a utility worker makes repairs near a red tagged home the RMS group is investigating Tuesday August 26, 2014. Risk Management Solutions (RMS) is a group of professionals that ... more

On Meadowbrook Drive in Napa, Calif. two PG&E workers consult near a buckled sidewalk where the RMS group is investigating Tuesday August 26, 2014. Risk Management Solutions (RMS) is a group of professionals that look at structural damage, liquefaction zones and interviews to determine the cost of the damage from an earthquake like the South Napa event. less

On Meadowbrook Drive in Napa, Calif. two PG&E workers consult near a buckled sidewalk where the RMS group is investigating Tuesday August 26, 2014. Risk Management Solutions (RMS) is a group of ... more

Napa County building inspectors David DeLong and Carl Bakken, in black, red tagging the Trefethen Family Vineyards winery building in Napa which suffered sever damage when the second floor shifted about four feet during the Sunday morning 6.0 magnitude earthquake. Built in 1886 the building was currently used as the winery's tasting room. August 26, 2014. less

Napa County building inspectors David DeLong and Carl Bakken, in black, red tagging the Trefethen Family Vineyards winery building in Napa which suffered sever damage when the second floor shifted about four ... more

Photo: Erik Castro, Special To The Chronicle

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A screen grab of the USGS Earthquake page showing recent earthquakes in American Canyon and Napa.

A screen grab of the USGS Earthquake page showing recent earthquakes in American Canyon and Napa.

Photo: Http://earthquake.usgs.gov/

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NAPA, CA - AUGUST 26: A for sale sign is posted on the back of an earthquake-damaged car on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries are continuing clean up operations. (Photo by Justin Sullivan/Getty Images) less

NAPA, CA - AUGUST 26: A for sale sign is posted on the back of an earthquake-damaged car on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries ... more

Photo: Justin Sullivan, Staff / Getty Images

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NAPA, CA - AUGUST 26: Jane Young moves a stack of bibles as she helps clean up the earthquake-damaged First Presbyterian Church on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries are continuing clean up operations. (Photo by Justin Sullivan/Getty Images) less

NAPA, CA - AUGUST 26: Jane Young moves a stack of bibles as she helps clean up the earthquake-damaged First Presbyterian Church on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked ... more

Workers from a national cleanup company assembled under the Hispanic Heritage mural Tuesday August 26, 2014. Cleanup continued in downtown Napa, Calif. following the large earthquake early Sunday morning.

Workers from a national cleanup company assembled under the Hispanic Heritage mural Tuesday August 26, 2014. Cleanup continued in downtown Napa, Calif. following the large earthquake early Sunday morning.

Residents and tourists paraded through downtown Napa, looking at many of the stores like this one which are red tagged. Cleanup continued in downtown Napa, Calif. following the large earthquake early Sunday morning. less

Residents and tourists paraded through downtown Napa, looking at many of the stores like this one which are red tagged. Cleanup continued in downtown Napa, Calif. following the large earthquake early Sunday ... more

A door way into the Trefethen Family Vineyards winery building in Napa which suffered sever damage when the second floor shifted about four feet during the Sunday morning 6.0 magnitude earthquake. Built in 1886 the building was currently used as the winery's tasting room. August 26, 2014. less

A door way into the Trefethen Family Vineyards winery building in Napa which suffered sever damage when the second floor shifted about four feet during the Sunday morning 6.0 magnitude earthquake. Built in 1886 ... more

Photo: Erik Castro, Special To The Chronicle

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NAPA, CA - AUGUST 26: Workers replace a broken window at a red tagged building that sustained earthquake damage on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries are continuing clean up operations. (Photo by Justin Sullivan/Getty Images) less

NAPA, CA - AUGUST 26: Workers replace a broken window at a red tagged building that sustained earthquake damage on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, ... more

Photo: Justin Sullivan, Getty Images

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NAPA, CA - AUGUST 26: Residents survey an earthquake-damaged street on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries are continuing clean up operations. (Photo by Justin Sullivan/Getty Images) *** BESTPIX *** less

NAPA, CA - AUGUST 26: Residents survey an earthquake-damaged street on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries are continuing clean ... more

Photo: Justin Sullivan, Getty Images

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City construction inspector Tina Chechourka applies an unsafe red tag on an apartment building on Third Street Tuesday, Aug. 26, 2014, in Napa, Calif. The earthquake that jolted California's wine capital may have caused at least $1 billion in property damage, but it also added impetus to the state's effort to develop an early warning system that might offer a few precious seconds for residents to duck under desks, trains to slow down and utility lines to be powered down before the seismic waves reach them. The magnitude-6.0 quake struck early Sunday near the city of Napa. (AP Photo/Eric Risberg) less

City construction inspector Tina Chechourka applies an unsafe red tag on an apartment building on Third Street Tuesday, Aug. 26, 2014, in Napa, Calif. The earthquake that jolted California's wine capital may ... more

Photo: Eric Risberg, Associated Press

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Seven-year-old Joey Bell helps clean out her mother's earthquake damaged hair salon as Stephanie Killingsworth, right, looks on Tuesday, Aug. 26, 2014, in Napa, Calif. The building that housed the salon was declared unsafe and red tagged. The earthquake that jolted California's wine capital may have caused at least $1 billion in property damage, but it also added impetus to the state's effort to develop an early warning system that might offer a few precious seconds for residents to duck under desks, trains to slow down and utility lines to be powered down before the seismic waves reach them. The magnitude-6.0 quake struck early Sunday near the city of Napa. (AP Photo/Eric Risberg) less

Seven-year-old Joey Bell helps clean out her mother's earthquake damaged hair salon as Stephanie Killingsworth, right, looks on Tuesday, Aug. 26, 2014, in Napa, Calif. The building that housed the salon was ... more

Photo: Eric Risberg, Associated Press

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NAPA, CA - AUGUST 26: Sanitation workers remove earthquake-damaged household items that were dropped off at Browns Valley Elementary School on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries are continuing clean up operations. (Photo by Justin Sullivan/Getty Images) less

NAPA, CA - AUGUST 26: Sanitation workers remove earthquake-damaged household items that were dropped off at Browns Valley Elementary School on August 26, 2014 in Napa, California. Two days after a 6.0 ... more

Photo: Justin Sullivan, Getty Images

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NAPA, CA - AUGUST 26: Pedestrians walk over a buckled section of sidewalk that was damaged during a 6.0 earthquake on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa Valley, residents and wineries are continuing clean up operations. (Photo by Justin Sullivan/Getty Images) less

NAPA, CA - AUGUST 26: Pedestrians walk over a buckled section of sidewalk that was damaged during a 6.0 earthquake on August 26, 2014 in Napa, California. Two days after a 6.0 earthquake rocked the Napa ... more

Photo: Justin Sullivan, Getty Images

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A 10-thousand gallon stainless steel tank at The Hess Collection winery in Napa that buckled liked a crushed soda can when the pressurized cabernet sauvignon burst out from a bottom opening during Sunday morning's 6.0 magnitude quake. August 26, 2014. less

A 10-thousand gallon stainless steel tank at The Hess Collection winery in Napa that buckled liked a crushed soda can when the pressurized cabernet sauvignon burst out from a bottom opening during Sunday ... more

Photo: Erik Castro, Special To The Chronicle

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Salvation Army volunteers and residents pray before dinner Monday at Napa Valley Mobile Home Park, which was damaged Sunday.

Salvation Army volunteers and residents pray before dinner Monday at Napa Valley Mobile Home Park, which was damaged Sunday.

Mayor Ed Lee (center) walked down Second Street during a brief tour of Napa Tuesday August 26, 2014. San Francisco Mayor Ed Lee got a tour of some of the downtown damage in Napa, Calif. due to the earthquake on Sunday. less

Mayor Ed Lee (center) walked down Second Street during a brief tour of Napa Tuesday August 26, 2014. San Francisco Mayor Ed Lee got a tour of some of the downtown damage in Napa, Calif. due to the earthquake on ... more

The Trefethen Family Vineyards winery building in Napa which suffered sever damage when the second floor shifted about four feet during the Sunday morning 6.0 magnitude earthquake. Built in 1886 the building was currently used as the winery's tasting room. August 26, 2014. less

The Trefethen Family Vineyards winery building in Napa which suffered sever damage when the second floor shifted about four feet during the Sunday morning 6.0 magnitude earthquake. Built in 1886 the building ... more

Browns Valley Market owner Larry Giovannoni looks out from his market which was badly damaged in the earthquake as he answers questions from the RMS team Tuesday August 26, 2014 in Napa, Calif. Risk Management Solutions (RMS) is a group of professionals that look at structural damage, liquefaction zones and interviews to determine the cost of the damage from an earthquake like the South Napa event. less

Browns Valley Market owner Larry Giovannoni looks out from his market which was badly damaged in the earthquake as he answers questions from the RMS team Tuesday August 26, 2014 in Napa, Calif. Risk Management ... more

Thirteen-year-old Nicholas Dillon lies in his hospital bed after being visited by Sacramento Republic FC player, and Napa native, Max Alvarez at UC Davis Medical Center in Sacramento, California, August 26, 2014. Dillon's pelvis was crushed by a falling chimney at his Napa home during Sunday's 6.0 magnitude earthquake.

As aftershocks from Sunday's powerful earthquake continued to rattle Wine Country on Tuesday, causing additional damage to a highway, local and state officials were assessing the toll of the quake and looking to the federal government for aid.

Estimated losses from ravaged homes, businesses and infrastructure in Napa and Vallejo were already in the tens of millions of dollars, state officials said, and the final tally is expected to top the federal threshold of about $51 million for luring valuable disaster funds from Washington.

Still, a decision on the money could be days or weeks out. Earthquakes, unlike hurricanes and other natural catastrophes, can be tougher to appraise for losses because of hidden damage - and can take longer to deem a national disaster.

"An earthquake impacts such a wide variety of businesses and people that have been affected by it, I think it is exactly what FEMA was meant to do, to get in and help and get a community up and running and functioning again," said Napa Mayor Jill Techel.

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Four earthquakes in southern Napa County on Tuesday morning marked the latest of more than 80 aftershocks following Sunday morning's 6.0-magnitude quake. The biggest woke residents at 5:33 a.m. - a 3.9-magnitude shaker about 2 miles northwest of American Canyon.

Most residents weren't rattled, noting that the aftershocks were nothing compared with the big temblor days ago.

"The dogs stayed on the bed, so I took my cue from them," said Napa resident Otto DeLeon, who was watching television early Tuesday during the aftershocks.

Highway 29 damage

But the shaking wasn't without consequence. The California Highway Patrol said Tuesday's seismic activity likely exacerbated damage along Highway 29, the main artery through Napa Valley, where a crack in the road at the George Butler Bridge over the Napa River prompted officers to close lanes temporarily for inspections.

The aftershocks came as Napa County residents were returning to some semblance of normalcy, with the Napa Valley Unified School District saying schools would reopen Wednesday.

All 30 properties under the Napa Unified School District passed inspection and were deemed safe after the district told students to stay home Monday and Tuesday so buildings could be surveyed, said district Superintendent Patrick Sweeney.

One independently operated school southwest of Napa, Stone Bridge Charter, will remain closed until next week. Inspectors found cracks in the floors and the walls and decided to keep home about 180 students in kindergarten through eighth grade until next week as a precaution.

San Francisco Mayor Ed Lee made the trip to Napa on Tuesday, telling local officials that the two cities were linked by tourism and pledging his support for the recovery.

"I will use my position as the mayor of San Francisco to ask for help and get corporations that are lucky to be in the position they are in in San Francisco to help us here as much as we can," he said.

As of Tuesday, 120 buildings in Napa had been red-tagged as too dangerous to enter, with roughly 500 yellow-tagged and in need of repairs. In the morning, the landmark Uptown Theatre in downtown Napa was red-tagged because of damage to the ceiling, walls and marquee.

In Vallejo, 12 buildings had been red-tagged and 75 had yellow tags.

Federal assistance could go a long way in helping homeowners and businesses as well as the government agencies responsible for repairing roads, schools and municipal buildings.

Under federal programs, homeowners without earthquake insurance generally qualify for as much as $30,000 in cash aid as well as low-interest loans up to $240,000 for making fixes and replacing property. Renters without insurance can get loans up to $40,000 to cover personal items.

Those who have earthquake insurance would be eligible for assistance to pay for uncovered losses. Only 5 percent of homeowners in the Napa area have earthquake insurance, according to the California Earthquake Authority, a state-run insurer that dominates the market.

Help for businesses

Business owners, meanwhile, could apply for low-interest loans to cover up to $2 million for earthquake damage under federal programs.

Government agencies, usually on the hook for much larger repair projects, would generally get 75 percent of their costs reimbursed by the government.

Officials with the Federal Emergency Management Agency, which advises the president on whether to provide disaster relief and to what degree, say they're waiting to hear how much help is needed.

"We're standing by ready to support the state, should they request our assistance," said FEMA spokesman Casey De Shong.

Even if local and state officials decide that help is needed, federal aid is not a lock.

Last year, FEMA initially rejected the governor's request to help cover damages from the Rim Fire, the catastrophic wildfire that burned through many Sierra communities and along the western edge of Yosemite National Park.

The state appealed the rejection, and the Obama administration ultimately agreed to assist with the recovery.